Chip carrier sockets are widely used for mounting the increasingly complex microprocessor chip carriers on circuit boards. It is well recognized that in view of the increasing miniaturization of electronic equipment including, in particular, computer processors, such chip carrier sockets must be of small size and of low profile to occupy a minimum of circuit board space and permit stacking of circuit boards in closely spaced, face-to-face relation while firmly mounting the chip carrier therein, reliably electrically connected to the circuit board. At the same time, the chip carrier sockets must be capable of manufacture at low cost and of application to the circuit board using economical mass production, automatic handling techniques.
In an attempt to meet such requirements, a widely known type of chip carrier socket comprises an insulating housing molded in one piece of plastic material with a rectangular frame-like body portion surrounding a central base-plate. The sides of the body portion are formed with respective rows of contact receiving cavities which open both inwardly towards a chip carrier receiving area within the profile of the frame-like body above the base-plate and downwardly to a lower, circuit board engaging face. Respective contacts are inserted into respective cavities through such lower face openings and force-fitted in the respective cavities with their contact spring portions extending through the inner openings in rows for establishing electrical connection to respective leads of rows of leads on respective sides of a rectangular chip carrier inserted into the chip carrier socket through an upper face, and with soldering tabs of the contacts extending inwardly of the frame-like body portion at the board engaging face for soldered connection by the common reflow soldering technique to respective soldering pads arranged closely spaced in rows on the circuit board.
In order to avoid heat produced during soldering being transferred from the soldered connections to the relatively thin base-plate and to afford access to the rows of tabs for a tool to correct any faulty soldering, respective perimetrical edges of the base-plate are located spaced apart from the respective adjacent sides of the frame body defining therebetween apertures aligned over the solder tabs. At the same time, the base-plate is spaced above the circuit board engaging face both to avoid deforming heat transfer thereto and to enable unimpeded washing of the board surface underneath the base-plate.
When connecting the chip carrier socket to the circuit board, the chip carrier socket is arranged on the circuit board and the solder tabs are pressed against the reflow-solder on the respective pads of the circuit board by pushing the frame-like body or the base-plate with a jig while heat is applied to the circuit board.
In one particular known construction, the base-plate is supported by the perimetrical edges thereof being joined to respective sides of the frame-like body portion by a series of bridges which extend spaced above and between adjacent of the contact tabs at substantially equally spaced apart intervals to each side of the frame-like body portion across the aperture thereby evenly supporting the base-plate at a multiplicity of closely spaced locations completely around its periphery conjointly to withstand forces applied thereto during insertion of the chip carrier into the chip carrier socket and stresses produced by the soldering process. Portions of the bridges adjoining the frame-like body portion are of increased height providing stand-offs supportingly engaging the underside of a chip carrier to maintain the chip carrier horizontal during insertion to obviate risk of damage to either the relatively weak base-plate, the contacts or to the bridges themselves arising from uneven insertion into the chip carrier socket.
However, a disadvantage of such known construction is that the the bridges span the rows of contact tabs and pads obstructing the field of view of a quality control inspector checking the accuracy of the soldering, particularly for solder bridges formed by the gel-like solder being forced between adjacent pads by the pressure applied during soldering. Such solder bridges may be hidden directly under the housing bridges as the housing bridges are located between adjacent tabs to avoid obstructing the insertion of the contacts into the cavities of the frame-like body. In addition, the presence of the bridges over the soldering rows may increase the possibility of solder wicking or otherwise being forced thereunder.
Furthermore, the presence of the bridges may hinder the free access of a soldering tool during correction of soldering faults with consequential increases in labor costs and slowing of production.